[mythtv-users] The Bigger... Disk contest, Fall 2007 edition
Brian Wood
beww at beww.org
Thu Oct 18 21:36:42 UTC 2007
f-myth-users at media.mit.edu wrote:
> > Date: Thu, 18 Oct 2007 13:35:31 -0600
> > From: Brian Wood <beww at beww.org>
>
> > I can only speak from my experience over many years. Whenever I have a
> > drive fail I put the dead one on my window sill. I have two piles, ATA
> > and SCSI. The ATA pile is about a foot high, the SCSI pile has one drive.
>
> [You never return them for the warrantee?]
It's just not worth the trouble IMHO. Stupid perhaps.
>
> Three massive problems with this approach, all related to sample bias
> (and otherwise known as "the plural of anecdote is NOT data"):
>
> (a) How many of each drive are in service? (That's "drives whose
> failures would cause them to wind up on your windowsill".) After
> all, if you've got 50 ATA drives and 3 SCSI drives, well...
> (b) Assuming that the answer to (a) is "half of each", then when's
> the last time you added to the ATA pile? [If it's "a long time
> ago", then maybe ATA reliability has increased (alternatively,
> perhaps SCSI reliability is decreasing... :)]
> (c) Are both types of drives subject to -exactly- the same sorts
> of service? Or are the SCSI drives in temperature-controlled
> machine-room racks and are never powered off, whereas the desktop
> drives get powered off every day and are in desktop machines that
> get moved around, dropped, kicked, or knocked over, and in which
> inquisitive little non-properly-ESD-protected hands occasionally
> reach in to reconfigure things? (Remember that a -lot- of what
> kills drives is powercycling and thermal cycling; remember also
> that desktops occasionally get tossed in a trunk, driven
> somewhere, and then plugged right back in even though they were
> brought to freezing and then not allowed to have all the
> condensation evaporate off and the disk platters rewarm back to
> nominal dimensions. Sure, that's bad, but I'd seen it. Also, the
> senior technical engineer of a company I know that makes massive
> disk-based stores for, e.g., banks told me that they routinely
> lose at least one disk in each huge array every time the array
> must be powercycled---despite using the most reliable disks they
> can get their hands on.)
>
> And yes, consult the CMU study; that's the one I was talking about
> when this came up here a few weeks/months ago.
All of your points are valid. The number of drives in service is about
equal.
The last failure as a SATA drive, but it was in a iMac machine with very
sub-optimum cooling.
But, as you might expect, the SCSI drives are in commercial-type servers
with good (and loud) cooling, and are almost never powered off, and the
AC power being supplied to them is well filtered and very clean. I also
think that commercial servers have power supplies that provide cleaner
DC output than most home PCs.
The PATA/ATA drives are in consumer-type cases, with less than optimum
cooling. They are powered off and on more often than the servers (though
still not very often) and are powered by consumer-type UPSs or straight
off the AC mains.
Plus, some of the consumer-type drives were purchased as re-furbs,
though I have noticed any difference between those and ones purchased new.
So it's not a fair test, I realize that.
For all I know the only difference between a modern SCSI drive and a
SATA one is the interface board. I know SCSI drives used to have better
bearings but I've heard that SATA drives are using the same ones.
I did find it interesting that Google's report indicated no major impact
from drive temperature, that goes against all the conventional wisdom
about electronic devices.
beww
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